Abstract. We study the evolution of circumbinary disks surrounding classical T Tau stars. High resolution numerical simulations are employed to model a system consisting of a central eccentric binary star within an accretion disk. The disk is assumed to be infinitesimally thin, however a detailed energy balance including viscous heating and radiative cooling is applied. A novel numerical approach using a parallelized Dual-Grid technique on two different coordinate systems has been implemented. Physical parameters of the setup are chosen to model the close system of DQ Tau and AK Sco, as well as the wider systems of GG Tau and UY Aur. Our main findings are for the tight binaries a substantial flow of material through the disk gap which is accreted onto the central stars in a phase dependent process. We are able to constrain the parameters of the systems by matching both accretion rates and derived spectral energy distributions to observational data where available.

Cytological aspects of hemiclonal (meroclonal) inheritance in diploid and triploid males of the hybridogenetic frog Rana esculenta (Rana ridibunda x Rana lessonae) have been studied by DNA flow cytometry. The fact that the R. ridibunda genome contains 16% more DNA than the R. lessonae genome provides the ability to discern cells containing genomes of any species from the water-frog complex under study. Data are presented showing that elimination of the R. ridibunda genome occurs in hybridogenetic males from certain populations. In triploid males, the cytogenetic mechanism of hemiclonal inheritance is simpler than in diploids: after the elimination of a genome (always the genome in the minority in the triploid set; "homogenizing elimination"), no compensatory duplication of the remaining genetic material is necessary, as it is in diploids. The process of elimination can be visualized in triploid males by using DNA flow cytometry to identify cells in the special phase of the spermatogonial cell cycle that we termed the E phase.

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